A blind-rivet nut such as described in German patent document No. 7,208,625 is a tubular fastener formed internally adjacent its one end with a screwthread and formed externally at its opposite end with a radially projecting flange or rim. It is used to provide a screwthread in thin material, for instance sheet metal, and can simultaneously join together two such workpieces in standard rivet fashion.
Such a fastener is set by means of a tool such as described in German patent No. 2,320,080 of L. Elflein having a head from whose tip projects the threaded end of a pulling rod that extends along an axis and that can move axially and rotate about this axis relative to the head. The fastener is threaded onto the end of the rod until the flange engages against the tip, and then is inserted through a hole in the workpiece or workpieces so that the threaded nut end lies well past the back face of the workpiece and the flange lies flat against the front workpiece face. The pulling rod then withdraws backward, pulling the threaded end of the rivet nut towards its flange and upsetting the rivet to the other side of the workpiece, forming an annular rim that engages the back face of the workpiece. This firmly seats the rivet nut in the workpiece. The pulling rod is then screwed back out of the nut.
A fastener that is screwed to this fastener will be much more solidly mounted than, for instance, it would have been if it were merely held in place with a sheet-metal screw or were a screwthread cut in in thin sheet material. In addition this fastener makes it possible to remove and reinsert the screw in it many times, which would not be possible in sheet material. In addition this fastener makes it possible to remove the reinsert the screw in it many times, which would not be possible in sheet metal, and this fastener can simultaneously hold together two workpiece sheets or plates while providing a convenient threaded seat.
The tools for setting such blind-rivet nuts are unfortunately relatively inconvenient to use. It is necessary to be able to rotate the pulling rod in either direction, albeit with limited torque, to mount the fastener on it before setting it and to separate the tool from it once it has been set. In addition this rod must be able to move backward into the head with considerable force to upset the fastener. These styles of motion must be conveniently controlled by the operator, especially as such fasteners are most frequently used in large mass-production operations where one person will set literally thousands of such rivets in a day.
Above-cited German patent document No. 7,208,625 provides a small pneumatic motor for rotating the pulling rod and for upsetting the rivet nut. The force needed to upset the rivet is, however, considerable when the rivet nut is of steel, so that this tool is of only limited use, that is with relatively soft rivets. It has however been found that when the rivet nut is made of a material such as aluminum that is soft enough to upset easily, the screwthreads are equally weak and are often stripped from it during the upsetting operation, leaving in the workpiece a poorly set rivet nut that has no threads. Another disadvantage of this device is that converting it from one size of rivet to another necessitates replacement of the entire core of the tool, a complex operation that is inherently costly due to duplication of much of the tool structure for each different rivet size one needs to deal with.
The setting gun of German patent No. 2,320,080 has an undescribed actuator for axial displacement of the pulling rod, and a wheel rotationally coupled to the pulling rod that projects from the side of the housing. To mount a rivet nut on the pulling rod, the nut is fitted with one hand over the end of the rod while the user's other hand holds the tool and strokes the wheel against some object like a wall, to set the rod in rotation. This obviously takes quite some dexterity. Once the rivet is set the wheel is reverse rotated to unscrew the rod from it, a purely manual operation that is far from efficient and that once again requires some dexterity or the mandrel will jam in the set rivet.
The assignee of the instant application markets two hydropneumatic rivet-nut setting guns having a hydropneumatic actuator and handle that extend at close to a right angle to the setting head. Once the rivet is mounted on the pulling rod, a trigger is actuated to fill a large pneumatic compartment associated with a hydraulic piston that effects a force multiplication and applies it to the pulling rod. The pulling rod projects out of the back of the setting head and carries a knob so that it can be rotated freely by hand in either direction, or it can be rotated by a small turbine built right into the setting head. The turbine can rotate in either of two directions, respective buttons being provided to effect such rotation.
Such a tool unfortunately is fairly difficult to operate. The manual model actually requires three hands or great dexterity to mount a rivet nut on the pull rod, and the nonmanual one still requires the manipulation of three different controls to set a single rivet. Only a dextrous and mechanically gifted person can operate these tools smoothly.
Another tool is known from my copending patent application Ser. No. 363,288 filed Mar. 29, 1982, now U.S. Pat. No. 4,515,005. This riveter serves for setting standard blind rivets and has a housing forming an air chamber and a liquid-filled hydraulic chamber adjacent thereto, a head on the housing having a tip and forming a liquid-filled working chamber communicating with the hydraulic chamber, and a working piston in the working chamber and carrying a chuck for grasping a mandrel of a blind rivet. The head and chuck form a passage having a front end opening at the tip and a rear end opening into a mandrel-catching compartment and the piston is displaceable in the working chamber between a ready position in which a mandrel of a blind rivet can be fitted into the passage at the chuck with the rivet engaged backwardly against the tip and an actuated position spaced from the tip and wherein the chuck is retracted. An air piston is provided in the air chamber and carries a hydraulic piston displaceable in the hydraulic chamber between an advanced position pressurizing the hydraulic and working chambers and corresponding to a front position of the air piston and a retracted position corresponding to a rear position of the air piston. The air chamber is pressurized to pressurize the working chamber and displace the chuck from the ready to the actuated position. Thus on displacement of the chuck from the former to the latter position the mandrel is pulled off the rivet at the tip. A valve is connected between the air chamber and the passage for feeding air under pressure from the air chamber to the nozzle after displacement of the chuck from the ready into the actuated position and for thereby simultaneously sucking the pulled-off mandrel from the chuck back along the passage into the compartment.
This tool is very convenient to use, but not suited for the setting of rivet nuts.